No I think you don't..
Just adjust these settings, click "Choose Images" and you'll get the links to them..
This image above is my test.. I didn't sign up.. just screenshot-ed it and then uploaded it to them.
However:
Quote:Terms of Use
What cannot be uploaded to Postimage.org servers:
Copyrighted images if you don't own copyright for it
Violence, racial intolerance, or advocate against any individual, group, or organization
Any other images that might be considered illegal in USA or EU countries
If you are not sure whether image you want to upload is allowed then do not upload that image. All uploaded images are checked by staff and images that violate terms will be removed without warning and uploader of such images might be banned from website.
Images embedded into third-party websites or emails should be wrapped in links back to the corresponding HTML pages at our site. Embedding images without such a link is not allowed. The outgoing link should lead the user directly to our web page without any interstitial pages or interruptions.
Automatic/programmatic uploads are not allowed. If you need image storage for your app, please use Amazon S3 or Google Cloud Storage. Violators may be hunted down and banned.
So, I'm guessing that it doesn't match our needs..
If I'm getting this right, all images stored there should lead to their site.. so we can't use it for advertising banners or stuff..